Rapid isolation of glomeruli coupled with gene expression profiling identifies downstream targets in Pod1 knockout mice

Stromal Transcription Factor 21 Regulates Development of the Renal Stroma via Interaction with Wnt/β-Catenin Signaling

Background

Kidney formation requires coordinated interactions between multiple cell types. Input from the interstitial progenitor cells is implicated in multiple aspects of kidney development. We previously reported that transcription factor 21 (Tcf21) is required for ureteric bud branching. Here, we show that Tcf21 in Foxd1+ interstitial progenitors regulates stromal formation and differentiation via interaction with β-catenin.

Methods

We utilized the Foxd1Cre;Tcf21f/f murine kidney for morphologic analysis. We used the murine clonal mesenchymal cell lines MK3/M15 to study Tcf21 interaction with Wnt/β-catenin.

Results

Absence of Tcf21 from Foxd1+ stromal progenitors caused a decrease in stromal cell proliferation, leading to marked reduction of the medullary stromal space. Lack of Tcf21 in the Foxd1+ stromal cells also led to defective differentiation of interstitial cells to smooth-muscle cells, perivascular pericytes, and mesangial cells. Foxd1Cre;Tcf21f/f kidney showed an abnormal pattern of the renal vascular tree. The stroma of Foxd1Cre;Tcf21f/f kidney demonstrated marked reduction in β-catenin protein expression compared with wild type. Tcf21 was bound to β-catenin both upon β-catenin stabilization and at basal state as demonstrated by immunoprecipitation in vitro. In MK3/M15 metanephric mesenchymal cells, Tcf21 enhanced TCF/LEF promoter activity upon β-catenin stabilization, whereas DNA-binding deficient mutated Tcf21 did not enhance TCF/LEF promoter activity. Kidney explants of Foxd1Cre;Tcf21f/f showed low mRNA expression of stromal Wnt target genes. Treatment of the explants with CHIR, a Wnt ligand mimetic, restored Wnt target gene expression. Here, we also corroborated previous evidence that normal development of the kidney stroma is required for normal development of the Six2+ nephron progenitor cells, loop of Henle, and the collecting ducts.

Conclusions

These findings suggest that stromal Tcf21 facilitates medullary stroma development by enhancing Wnt/β-catenin signaling and promotes stromal cell proliferation and differentiation. Stromal Tcf21 is also required for the development of the adjacent nephron epithelia.

The ShGlomAssay Combines High-Throughput Drug Screening With Downstream Analyses and Reveals the Protective Role of Vitamin D3 and Calcipotriol on Podocytes

Chronic kidney disease (CKD) is a major public health burden affecting more than 500 million people worldwide. Podocytopathies are the main cause for the majority of CKD cases due to pathogenic morphological as well as molecular biological alterations of postmitotic podocytes. Podocyte de-differentiation is associated with foot process effacement subsequently leading to proteinuria. Since currently no curative drugs are available, high throughput screening methods using a small number of animals are a promising and essential tool to identify potential drugs against CKD in the near future. Our study presents the implementation of the already established mouse GlomAssay as a semi-automated high-throughput screening method-shGlomAssay-allowing the analysis of several hundreds of FDA-verified compounds in combination with downstream pathway analysis like transcriptomic and proteomic analyses from the same samples, using a small number of animals. In an initial prescreening we have identified vitamin D3 and its analog calcipotriol to be protective on podocytes. Furthermore, by using RT-qPCR, Western blot, and RNA sequencing, we found that mRNA and protein expression of nephrin, the vitamin D receptor and specific podocyte markers were significantly up-regulated due to vitamin D3- and calcipotriol-treatment. In contrast, kidney injury markers were significantly down-regulated. Additionally, we found that vitamin D3 and calcipotriol have had neither influence on the expression of the miR-21 and miR-30a nor on miR-125a/b, a miRNA described to regulate the vitamin D receptor. In summary, we advanced the established mouse GlomAssay to a semi-automated high-throughput assay and combined it with downstream analysis techniques by using only a minimum number of animals. Hereby, we identified the vitamin D signaling pathway as podocyte protective and to be counteracting their de-differentiation.

Nephrotoxicity of perfluorooctane sulfonate (PFOS)-effect on transcription and epigenetic factors

Perfluorooctane sulfonate (PFOS) is a widespread persistent environmental pollutant implicated in nephrotoxicity with altered metabolism, carcinogenesis, and fibrosis potential. We studied the underlying epigenetic mechanism involving transcription factors of PFOS-induced kidney injury. A 14-day orally dosed mouse model was chosen to study acute influences in vivo. Messenger RNA expression analysis and gene set enrichment analysis were performed to elucidate the relationship between epigenetic regulators, transcription factors, kidney disease, and metabolism homeostasis. PFOS was found to accumulate in mouse kidney in a dose-dependent manner. Kidney injury markers Acta2 and Bcl2l1 increased in expression significantly. Transcription factors, including Nef2l2, Hes1, Ppara, and Ppard, were upregulated, while Smarca2 and Pparg were downregulated. Furthermore, global DNA methylation levels decreased and the gene expression of histone demethylases Kdm1a and Kdm4c were upregulated. Our work implicates PFOS-induced gene expression alterations in epigenetics, transcription factors, and kidney biomarkers with potential implications for kidney fibrosis and kidney carcinogenesis. Future experiments can focus on epigenetic mechanisms to establish a panel of PFOS-induced biomarkers for nephrotoxicity evaluation.

GWAS in Mice Maps Susceptibility to HIV-Associated Nephropathy to the Ssbp2 Locus

BACKGROUND

To gain insight into the pathogenesis of collapsing glomerulopathy, a rare form of FSGS that often arises in the setting of viral infections, we performed a genome-wide association study (GWAS) among inbred mouse strains using a murine model of HIV-1 associated nephropathy (HIVAN).

METHODS

We first generated F1 hybrids between HIV-1 transgenic mice on the FVB/NJ background and 20 inbred laboratory strains. Analysis of histology, BUN, and urinary NGAL demonstrated marked phenotypic variation among the transgenic F1 hybrids, providing strong evidence for host genetic factors in the predisposition to nephropathy. A GWAS in 365 transgenic F1 hybrids generated from these 20 inbred strains was performed.

RESULTS

We identified a genome-wide significant locus on chromosome 13-C3 and multiple additional suggestive loci. Crossannotation of the Chr. 13 locus, including single-cell transcriptomic analysis of wildtype and HIV-1 transgenic mouse kidneys, nominated Ssbp2 as the most likely candidate gene. Ssbp2 is highly expressed in podocytes, encodes a transcriptional cofactor that interacts with LDB1 and LMX1B, which are both previously implicated in FSGS. Consistent with these data, older Ssbp2 null mice spontaneously develop glomerulosclerosis, tubular casts, interstitial fibrosis, and inflammation, similar to the HIVAN mouse model.

CONCLUSIONS

These findings demonstrate the utility of GWAS in mice to uncover host genetic factors for rare kidney traits and suggest Ssbp2 as susceptibility gene for HIVAN, potentially acting via the LDB1-LMX1B transcriptional network.

Patient-Derived Orthotopic Xenograft (PDOX) Mouse Models of Primary and Recurrent Meningioma

BACKGROUND

Meningiomas constitute one-third of all primary brain tumors. Although typically benign, about 20% of these tumors recur despite surgery and radiation, and may ultimately prove fatal. There are currently no effective chemotherapies for meningioma. We, therefore, set out to develop patient-derived orthotopic xenograft (PDOX) mouse models of human meningioma using tumor.

METHOD

Of nine patients, four had World Health Organization (WHO) grade I tumors, five had WHO grade II tumors, and in this second group two patients also had recurrent (WHO grade III) meningioma. We also classified the tumors according to our recently developed molecular classification system (Types A, B, and C, with C being the most aggressive). We transplanted all 11 surgical samples into the skull base of immunodeficient (SCID) mice. Only the primary and recurrent tumor cells from one patient-both molecular Type C, despite being WHO grades II and III, respectively-led to the formation of meningioma in the resulting mouse models. We characterized the xenografts by histopathology and RNA-seq and compared them with the original tumors. We performed an in vitro drug screen using 60 anti-cancer drugs followed by in vivo validation.

RESULTS

The PDOX models established from the primary and recurrent tumors from patient K29 (K29P-PDOX and K29R-PDOX, respectively) replicated the histopathology and key gene expression profiles of the original samples. Although these xenografts could not be subtransplanted, the cryopreserved primary tumor cells were able to reliably generate PDOX tumors. Drug screening in K29P and K29R tumor cell lines revealed eight compounds that were active on both tumors, including three histone deacetylase (HDAC) inhibitors. We tested the HDAC inhibitor Panobinostat in K29R-PDOX mice, and it significantly prolonged mouse survival (p < 0.05) by inducing histone H3 acetylation and apoptosis.

CONCLUSION

Meningiomas are not very amenable to PDOX modeling, for reasons that remain unclear. Yet at least some of the most malignant tumors can be modeled, and cryopreserved primary tumor cells can create large panels of tumors that can be used for preclinical drug testing.

Transcription Factor 21 Is Required for Branching Morphogenesis and Regulates the Gdnf-Axis in Kidney Development

BACKGROUND

The mammalian kidney develops through reciprocal inductive signals between the metanephric mesenchyme and ureteric bud. Transcription factor 21 (Tcf21) is highly expressed in the metanephric mesenchyme, including Six2-expressing cap mesenchyme and Foxd1-expressing stromal mesenchyme. Tcf21 knockout mice die in the perinatal period from severe renal hypodysplasia. In humans, Tcf21 mRNA levels are reduced in renal tissue from human fetuses with renal dysplasia. The molecular mechanisms underlying these renal defects are not yet known.

METHODS

Using a variety of techniques to assess kidney development and gene expression, we compared the phenotypes of wild-type mice, mice with germline deletion of the Tcf21 gene, mice with stromal mesenchyme-specific Tcf21 deletion, and mice with cap mesenchyme-specific Tcf21 deletion.

RESULTS

Germline deletion of Tcf21 leads to impaired ureteric bud branching and is accompanied by downregulated expression of Gdnf-Ret-Wnt11, a key pathway required for branching morphogenesis. Selective removal of Tcf21 from the renal stroma is also associated with attenuation of the Gdnf signaling axis and leads to a defect in ureteric bud branching, a paucity of collecting ducts, and a defect in urine concentration capacity. In contrast, deletion of Tcf21 from the cap mesenchyme leads to abnormal glomerulogenesis and massive proteinuria, but no downregulation of Gdnf-Ret-Wnt11 or obvious defect in branching.

CONCLUSIONS

Our findings indicate that Tcf21 has distinct roles in the cap mesenchyme and stromal mesenchyme compartments during kidney development and suggest that Tcf21 regulates key molecular pathways required for branching morphogenesis.

AT2 R deficiency mediated podocyte loss via activation of ectopic hedgehog interacting protein (Hhip) gene expression

Angiotensin II type 2 receptor (AT₂ R) deficiency in AT₂ R knockout (KO) mice has been linked to congenital abnormalities of the kidney and urinary tract; however, the mechanisms by which this occurs are poorly understood. In this study, we examined whether AT₂ R deficiency impaired glomerulogenesis and mediated podocyte loss/dysfunction in vivo and in vitro. Nephrin-cyan fluorescent protein (CFP)-transgenic (Tg) and Nephrin/AT₂ RKO mice were used to assess glomerulogenesis, while wild-type and AT₂ RKO mice were used to evaluate maturation of podocyte morphology/function. Immortalized mouse podocytes (mPODs) were employed for in vitro studies. AT₂ R deficiency resulted in diminished glomerulogenesis in E15 embryos, but had no impact on actual nephron number in neonates. Pups lacking AT₂ R displayed features of renal dysplasia with lower glomerular tuft volume and podocyte numbers. In vivo and in vitro studies demonstrated that loss of AT₂ R was associated with elevated NADPH oxidase 4 levels, which in turn stimulated ectopic hedgehog interacting protein (Hhip) gene expression in podocytes. Consequently, ectopic Hhip expression activation either triggers caspase-3 and p53-related apoptotic processes resulting in podocyte loss, or activates TGFβ1-Smad2/3 cascades and α-SMA expression to transform differentiated podocytes to undifferentiated podocyte-derived fibrotic cells. We analyzed HHIP expression in the kidney disease database (Nephroseq) and then validated this using HHIP immunohistochemistry staining of human kidney biopsies (controls versus focal segmental glomerulosclerosis). In conclusion, loss of AT₂ R is associated with podocyte loss/dysfunction and is mediated, at least in part, via augmented ectopic Hhip expression in podocytes. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A novel assay to assess the effect of pharmaceutical compounds on the differentiation of podocytes

BACKGROUND AND PURPOSE

Therapeutic options for treating glomerulopathies, the main cause of chronic kidney disease, are limited. Podocyte dedifferentiation is a major event in the pathogenesis of glomerulopathies. The goal of the present study was, therefore, to develop an assay to monitor podocyte differentiation suitable for compound screening.

EXPERIMENTAL APPROACH

We isolated and cultured glomeruli from transgenic mice, expressing cyan fluorescent protein (CFP) under the control of the promoter of nephrin, a marker of podocyte differentiation. Mean CFP fluorescence intensity per glomerulus (MFG) was determined by summation of all glomerular voxels from confocal z-stacks in the absence and presence of pharmaceutical compounds.

KEY RESULTS

In untreated cultured glomeruli, MFG remained fairly stable during the first 5 days, when foot processes were already effaced, and the level of many podocyte-specific proteins was only mildly affected, as revealed by proteomics. Between day 6 and 9, MFG decreased to almost zero. The decrease in MFG was paralleled by a decrease in CFP and nephrin expression, as determined by RT-PCR, western blots and proteomics. Puromycin aminonucleoside (PAN), which damages podocytes, concentration-dependently induced a complete loss of MFG. Dexamethasone (25 μM) and pioglitazone (10 μM) markedly attenuated the effect of 0.6 μg·mL^-1 PAN on MFG.

CONCLUSION AND IMPLICATIONS

In summary, we established a novel assay to assess the effect of pharmaceutical compounds on the differentiation of podocytes in situ. Our assay is suitable for compound screening to identify drugs for the treatment of glomerulopathies.

Podocytes

Podocytes are highly specialized cells of the kidney glomerulus that wrap around capillaries and that neighbor cells of the Bowman’s capsule. When it comes to glomerular filtration, podocytes play an active role in preventing plasma proteins from entering the urinary ultrafiltrate by providing a barrier comprising filtration slits between foot processes, which in aggregate represent a dynamic network of cellular extensions. Foot processes interdigitate with foot processes from adjacent podocytes and form a network of narrow and rather uniform gaps. The fenestrated endothelial cells retain blood cells but permit passage of small solutes and an overlying basement membrane less permeable to macromolecules, in particular to albumin. The cytoskeletal dynamics and structural plasticity of podocytes as well as the signaling between each of these distinct layers are essential for an efficient glomerular filtration and thus for proper renal function. The genetic or acquired impairment of podocytes may lead to foot process effacement (podocyte fusion or retraction), a morphological hallmark of proteinuric renal diseases. Here, we briefly discuss aspects of a contemporary view of podocytes in glomerular filtration, the patterns of structural changes in podocytes associated with common glomerular diseases, and the current state of basic and clinical research.

TCF21 hypermethylation in genetically quiescent clear cell sarcoma of the kidney

Clear Cell Sarcoma of the Kidney (CCSK) is a rare childhood tumor whose molecular pathogenesis remains poorly understood. We analyzed a discovery set of 13 CCSKs for changes in chromosome copy number, mutations, rearrangements, global gene expression and global DNA methylation. No recurrent segmental chromosomal copy number changes or somatic variants (single nucleotide or small insertion/deletion) were identified. One tumor with t(10;17)(q22;p13) involving fusion of YHWAE with NUTM2B was identified. Integrated analysis of expression and methylation data identified promoter hypermethylation and low expression of the tumor suppressor gene TCF21 (Pod-1/capsulin/epicardin) in all CCSKs except the case with t(10;17)(q22;p13). TARID, the long noncoding RNA responsible for demethylating TCF21, was virtually undetectable in most CCSKs. TCF21 hypermethylation and decreased TARID expression were validated in an independent set of CCSK tumor samples. The presence of significant hypermethylation of TCF21, a transcription factor known to be active early in renal development, supports the hypothesis that hypermethylation of TCF21 and/or decreased TARID expression lies within the pathogenic pathway of most CCSKs. Future studies are needed to functionally verify a tumorigenic role of TCF21 down-regulation and to tie this to the unique gene expression pattern of CCSK.

Surface modification of multiwall carbon nanotubes determines the pro-inflammatory outcome in macrophage

Carbon nanotubes (CNTs) are widely used in industry and biomedicine. While several studies have focused on biological matters, attempts to systematically elucidate the toxicity mechanisms of CNTs are limited. The aim of the present study was to evaluate and compare the cytotoxicity of raw multi-walled carbon nanotubes (MWCNTs) and MWCNTs functionalized with carboxylation (MWCNTs-COOH) or polyethylene glycol (MWCNTs-PEG) in murine macrophages. Our results show that only MWCNTs-COOH and raw MWCNTs alter the oxidative potential of macrophages by increasing reactive oxygen species and the expression of pro-inflammatory factors in both a concentration- and surface coating-dependent manner. The data suggest that compare with raw MWCNTs and MWCNTs-PEG, the MWCNTs-COOH produces a significant increase in ROS generation, interruption of ATP synthesis, and activation of the MAPK and NF-κB signaling pathways, which in turn upregulates IL-1β, IL-6, TNF-α, and iNOS to trigger cell death. These findings suggest that contributory cellar uptake caused by physicochemical factors rather than residual metal catalysts plays a role in ROS-mediated pro-inflammatory responses in vitro.

Compartment-specific flow cytometry for the analysis of TNF-mediated recruitment and activation of glomerular leukocytes in murine kidneys

Cytokines of the TNF superfamily, particularly TNF itself, are important mediators of inflammatory leukocyte recruitment and activation in parenchymal organs. In inflammatory kidney diseases, leukocytes accumulate in glomeruli and the tubulointerstitium, leading to glomerulonephritis and tubulointerstitial nephritis, respectively. In particular, glomeruli can be the target of organ-threatening leukocyte-mediated inflammation. As microvasculatures of the glomerulus and the tubulointerstitium differ markedly in their structural and functional properties, recruitment and subsequent activation of leukocytes to these sites occur via distinct mechanisms. To understand the pathways and mediators of leukocyte-driven inflammation in the kidney it is therefore essential to analyze glomerular and tubulointerstitial leukocyte recruitment in a compartment-specific way. The protocol presented here describes an easy and rapid technique that allows compartment-specific quantitation and qualitative analysis of leukocytes present in glomeruli and tubulointerstitial tissue by flow cytometry after separation of these tissue compartments.

Glomerular development--shaping the multi-cellular filtration unit

The glomerulus represents a highly structured filtration unit, composed of glomerular endothelial cells, mesangial cells, podocytes and parietal epithelial cells. During glomerulogenesis an intricate network of signaling pathways involving transcription factors, secreted factors and cell-cell communication is required to guarantee accurate evolvement of a functional, complex 3-dimensional glomerular architecture. Here, we want to provide an overview on the critical steps and relevant signaling cascades of glomerular development.

TGF-β-activated kinase 1 is crucial in podocyte differentiation and glomerular capillary formation

TGF-β-activated kinase 1 (TAK1) is a key intermediate in signal transduction induced by TGF-β or inflammatory cytokines, such as TNF-α and IL-1, which are potent inducers of podocyte injury responses that lead to proteinuria and glomerulosclerosis. Nevertheless, little is known about the physiologic and pathologic roles of TAK1 in podocytes. To examine the in vivo role of TAK1, we generated podocyte-specific Tak1 knockout mice (Nphs2-Cre(+):Tak1(fx/fx); Tak1(∆/∆)). Targeted deletion of Tak1 in podocytes resulted in perinatal lethality, with approximately 50% of animals dying soon after birth and 90% of animals dying within 1 week of birth. Tak1(∆/∆) mice developed proteinuria from P1 and exhibited delayed glomerulogenesis and reduced expression of Wilms' tumor suppressor 1 and nephrin in podocytes. Compared with Tak1(fx/fx) mice, Tak1(∆/∆) mice exhibited impaired formation of podocyte foot processes that caused disruption of the podocyte architecture with prominent foot process effacement. Intriguingly, Tak1(∆/∆) mice displayed increased expression of vascular endothelial growth factor within the glomerulus and abnormally enlarged glomerular capillaries. Furthermore, 4- and 7-week-old Tak1(∆/∆) mice with proteinuria had increased collagen deposition in the mesangium and the adjacent tubulointerstitial area. Thus, loss of Tak1 in podocytes is associated with the development of proteinuria and glomerulosclerosis. Taken together, our data show that TAK1 regulates the expression of Wilms' tumor suppressor 1, nephrin, and vascular endothelial growth factor and that TAK1 signaling has a crucial role in podocyte differentiation and attainment of normal glomerular microvasculature during kidney development and glomerular filtration barrier homeostasis.

In vivo imaging of kidney glomeruli transplanted into the anterior chamber of the mouse eye

Multiphoton microscopy enables live imaging of the renal glomerulus. However, repeated in vivo imaging of the same glomerulus over extended periods of time and the study of glomerular function independent of parietal epithelial and proximal tubular cell effects has not been possible so far. Here, we report a novel approach for non-invasive imaging of acapsular glomeruli transplanted into the anterior chamber of the mouse eye. After microinjection, glomeruli were capable of engrafting on the highly vascularized iris. Glomerular structure was preserved, as demonstrated by podocyte specific expression of cyan fluorescent protein and by electron microscopy. Injection of fluorescence-labeled dextrans of various molecular weights allowed visualization of glomerular filtration and revealed leakage of 70 kDa dextran in an inducible model of proteinuria. Our findings demonstrate functionality and long-term survival of glomeruli devoid of Bowman's capsule and provide a novel approach for non-invasive longitudinal in vivo study of glomerular physiology and pathophysiology.

Early B-cell factor 1 is an essential transcription factor for postnatal glomerular maturation

The coordination of multiple cytokines and transcription factors with their downstream signaling pathways have been shown to be integral to nephron maturation. Here we present a completely novel role for the helix-loop-helix transcription factor Early B cell Factor 1 (Ebf1), originally identified for B cell maturation, for the proper maturation of glomerular cells from mesenchymal progenitors. The expression of Ebf1 was both spatially and temporally regulated within the developing cortex and glomeruli. Using Ebf1-null mice we then identified biochemical, metabolic, and histological abnormalities in renal development that arose in the absence of this transcription factor. In the Ebf1 knockout mice the developed kidneys show thinned cortices and reduced glomerular maturation. The glomeruli showed abnormal vascularization and severely effaced podocytes. The mice exhibited early albuminuria and elevated blood urea nitrogen levels. Moreover, the GFR was reduced over 66 percent and the expression of podocyte-derived VEGF-A was decreased compared to wild type control mice. Thus, Ebf1 has a significant and novel role in glomerular development, podocyte maturation, and the maintenance of kidney integrity and function.

miRNA expression pattern associated with prognosis in elderly patients with advanced OPSC and OCC

The long-term survival for elderly patients with advanced ovarian papillary serous carcinoma (OPSC) does not exceed 30%, and the incidence and prognosis rise continuously after menopause. The aim of this study was to identify the differences in key miRNAs and their potential regulators through miRNA microarray analysis, functional target prediction, and clinical outcome between the elderly patients with advanced OPSC and ovarian clear cell carcinoma (OCC) who all suffered poor prognosis, to identify the pathogenetic basis, and to improve the understanding of the molecular basis of advanced OPCS in elderly patients. Through microarray analysis, we found 52 unique miRNAs with significant fold‑change in expression levels, of which 9 were upregulated, whereas 43 were downregulated in OCC patients compared to elderly OPSC patients with advanced stage. Among these prediction miRNAs, miR-30a, miR-30e and miR-505 were found to have some common cancer-related targets. Lower expression of these three miRNAs of advanced OPSC in elderly patients, all associated with significantly poorer survival rate, strongly suggesting that they could be critical oncogenes and take important roles in OPSC etiology in elderly patients with advantaged stage. Functional analyses support the above hypothesis. Their targets, ATF3, STMN1 and MYC suggest that OPSC also has aggressive biological behavior when presented with advanced stage, and support the epidemiology results that incidence and mortality of advanced OPSC increases continuously. miR-30a, miR-30e and miR-505 may be important pathogenetic factors for OPSC in elderly patients with advanced stage. Age could be regarded as a continuous covariate in this process. This may improve the understanding of molecular underpinnings of advanced OPSC in elderly patients, and provide improved diagnostic, prognostic and therapeutic approaches.

Tcf21 regulates the specification and maturation of proepicardial cells

The epicardium is a mesothelial cell layer essential for vertebrate heart development and pertinent for cardiac repair post-injury in the adult. The epicardium initially forms from a dynamic precursor structure, the proepicardial organ, from which cells migrate onto the heart surface. During the initial stage of epicardial development crucial epicardial-derived cell lineages are thought to be determined. Here, we define an essential requirement for transcription factor Tcf21 during early stages of epicardial development in Xenopus, and show that depletion of Tcf21 results in a disruption in proepicardial cell specification and failure to form a mature epithelial epicardium. Using a mass spectrometry-based approach we defined Tcf21 interactions and established its association with proteins that function as transcriptional co-repressors. Furthermore, using an in vivo systems-based approach, we identified a panel of previously unreported proepicardial precursor genes that are persistently expressed in the epicardial layer upon Tcf21 depletion, thereby confirming a primary role for Tcf21 in the correct determination of the proepicardial lineage. Collectively, these studies lead us to propose that Tcf21 functions as a transcriptional repressor to regulate proepicardial cell specification and the correct formation of a mature epithelial epicardium.

Synchronous detection of miRNAs, their targets and downstream proteins in transferred FFPE sections: applications in clinical and basic research

After discovering new miRNAs, it is often difficult to determine their targets and effects on downstream protein expression. In situ hybridization (ISH) and immunohistochemistry (IHC) are two commonly used methods for clinical diagnosis and basic research. We used an optimized technique that simultaneously detects miRNAs, their binding targets and corresponding proteins on transferred serial formalin fixed paraffin embedded (FFPE) sections from patients. Combined with bioinformatics, this method was used to validate the reciprocal expression of specific miRNAs and targets that were detected by ISH, as well as the expression of downstream proteins that were detected by IHC. A complete analysis was performed using a limited number of transferred serial FFPE sections that had been stored for 1-4 years at room temperature. Some sections had even been previously stained with H&E. We identified a miRNA that regulates epithelial ovarian cancer, along with its candidate target and related downstream protein. These findings were directly validated using sub-cellular components obtained from the same patient sample. In addition, the expression of Nephrin (a podocyte marker) and Stmn1 (a recently identified marker related to glomerular development) were confirmed in transferred FFPE sections of mouse kidney. This procedure may be adapted for clinical diagnosis and basic research, providing a qualitative and efficient method to dissect the detailed spatial expression patterns of miRNA pathways in FFPE tissue, especially in cases where only a small biopsy sample can be obtained.

A new Cre driver mouse line, Tcf21/Pod1-Cre, targets metanephric mesenchyme

Conditional gene targeting in mice has provided great insight into the role of gene function in kidney development and disease. Although a number of Cre-driver mouse strains already exist for the kidney, development of additional strains with unique expression patterns is needed. Here we report the generation and validation of a Tcf21/Pod1-Cre driver strain that expresses Cre recombinase throughout the condensing and stromal mesenchyme of developing kidneys and in their derivatives including epithelial components of the nephron and interstitial cells. To test the efficiency of this line, we crossed it to mice transgenic for either loss or gain of function β-catenin conditional alleles. Mice with deletion of β-catenin from Tcf21-expressing cells are born with hypoplastic kidneys, hydroureters and hydronephrosis. By contrast, Tcf21-Cre driven gain of function for β-catenin in mice results in fused midline kidneys and hypoplastic kidneys. Finally, we report the first renal mesenchymal deletion of Patched1 (Ptch1), the receptor for sonic hedgehog (Shh), which results in renal cysts demonstrating a functional role of Shh signaling pathway in renal cystogensis. In summary, we report the generation and validation of a new Cre driver strain that provides robust excision in metanephric mesenchyme.

Inhibition of MTOR disrupts autophagic flux in podocytes

Inhibitors of the mammalian target of rapamycin (MTOR) belong to a family of drugs with potent immunosuppressive, antiangiogenic, and antiproliferative properties. De novo or worsening proteinuria can occur during treatment with these agents, but the mechanism by which this occurs is unknown. We generated and characterized mice carrying a podocyte-selective knockout of the Mtor gene. Although Mtor was dispensable in developing podocytes, these mice developed proteinuria at 3 weeks and end stage renal failure by 5 weeks after birth. Podocytes from these mice exhibited an accumulation of the autophagosome marker LC3 (rat microtubule-associated protein 1 light chain 3), autophagosomes, autophagolysosomal vesicles, and damaged mitochondria. Similarly, human podocytes treated with the MTOR inhibitor rapamycin accumulated autophagosomes and autophagolysosomes. Taken together, these results suggest that disruption of the autophagic pathway may play a role in the pathogenesis of proteinuria in patients treated with MTOR inhibitors.

Cell biology and pathology of podocytes

As an integral member of the filtration barrier in the kidney glomerulus, the podocyte is in a unique geographical position: It is exposed to chemical signals from the urinary space (Bowman's capsule), it receives and transmits chemical and mechanical signals to/from the glomerular basement membrane upon which it elaborates, and it receives chemical and mechanical signals from the vascular space with which it also communicates. As with every cell, the ability of the podocyte to receive signals from the surrounding environment and to translate them to the intracellular milieu is dependent largely on molecules residing on the cell membrane. These molecules are the first-line soldiers in the ongoing battle to sense the environment, to respond to friendly signals, and to defend against injurious foes. In this review, we take a membrane biologist's view of the podocyte, examining the many membrane receptors, channels, and other signaling molecules that have been implicated in podocyte biology. Although we attempt to be comprehensive, our goal is not to capture every membrane-mediated pathway but rather to emphasize that this approach may be fruitful in understanding the podocyte and its unique properties.

Circulating endoglin concentration is not elevated in chronic kidney disease

BACKGROUND

Soluble endoglin, a TGF-β receptor, plays a key role in cardiovascular physiology. Whether circulating concentrations of soluble endoglin are elevated in CKD or underlie the high risk of cardiovascular death associated with chronic kidney disease (CKD) is unknown.

METHODS

Individuals with and without CKD were recruited at a single center. Estimated glomerular filtration rate (eGFR) was estimated using the modified MDRD study equation and the serum creatinine at the time of recruitment, and patients were assigned to specific CKD stage according to usual guidelines. Serum endoglin concentration was measured by ELISA and univariate and multivariable regression was used to analyze the association between eGFR or CKD stage and the concentration of soluble endoglin.

RESULTS

Serum endoglin was measured in 216 patients including 118 with stage 3 or higher CKD and 9 individuals with end stage renal disease (ESRD). Serum endoglin concentration did not vary significantly with CKD stage (increase of 0.16 ng/mL per 1 stage increase in CKD, P = 0.09) or eGFR (decrease -0.06 ng/mL per 10 mL/min/1.73 m(2) increase in GFR, P = 0.12), and was not higher in individuals with ESRD than in individuals with preserved renal function (4.2±1.1 and 4.3±1.2 ng/mL, respectively). Endoglin concentration was also not significantly associated with urinary albumin excretion.

CONCLUSIONS

Renal function is not associated with the circulating concentration of soluble endoglin. Elevations in soluble endoglin concentration are unlikely to contribute to the progression of CKD or the predisposition of individuals with CKD to develop cardiovascular disease.

Differential gene expression profiling of oesophageal squamous cell carcinoma by DNA microarray and bioinformatics analysis

Differential gene expression profiling was carried out on primary tumour tissues and adjacent non-neoplastic tissues from patients with oesophageal squamous cell carcinoma (ESCC). RNA extracted from ESCC tissues and matched normal oesophageal epithelium of four ESCC patients was analysed using whole-genome microarrays. Bioinformatics analysis was also carried out to ascertain which genes and pathways may be important in the carcinogenesis of ESCC. A total of 570 genes were identified that differed significantly in expression: 303 genes were up-regulated and 267 genes were down-regulated in ESCC tissues compared with normal oesophageal epithelium. Gene ontology analysis showed that the primary molecular functions of these genes were related to the extracellular region, collagen and endopeptidase inhibitor activity. Pathway analysis revealed seven pathways or networks highly associated with the differential expression profile. Gene set analysis showed that the POD1_KO_UP gene set was significantly enriched, containing 15 matching genes. Thus, a large number of genes are involved in the carcinogenesis of ESCC and participate in various cell processes and pathways.

Insulin signaling to the glomerular podocyte is critical for normal kidney function

Diabetic nephropathy (DN) is the leading cause of renal failure in the world. It is characterized by albuminuria and abnormal glomerular function and is considered a hyperglycemic "microvascular" complication of diabetes, implying a primary defect in the endothelium. However, we have previously shown that human podocytes have robust responses to insulin. To determine whether insulin signaling in podocytes affects glomerular function in vivo, we generated mice with specific deletion of the insulin receptor from their podocytes. These animals develop significant albuminuria together with histological features that recapitulate DN, but in a normoglycemic environment. Examination of "normal" insulin-responsive podocytes in vivo and in vitro demonstrates that insulin signals through the MAPK and PI3K pathways via the insulin receptor and directly remodels the actin cytoskeleton of this cell. Collectively, this work reveals the critical importance of podocyte insulin sensitivity for kidney function.

A molecular profile of focal segmental glomerulosclerosis from formalin-fixed, paraffin-embedded tissue

Focal segmental glomerulosclerosis (FSGS) is a common form of idiopathic nephrotic syndrome defined by the characteristic lesions of focal glomerular sclerosis and foot process effacement; however, its etiology and pathogenesis are unknown. We used mRNA isolated from laser-captured glomeruli from archived formalin-fixed, paraffin-embedded renal biopsies, until recently considered an unsuitable source of mRNA for microarray analysis, to investigate the glomerular gene expression profiles of patients with primary classic FSGS, collapsing FSGS (COLL), minimal change disease (MCD), and normal controls (Normal). Amplified mRNA was hybridized to an Affymetrix Human X3P array. Unsupervised (unbiased) hierarchical clustering revealed two distinct clusters delineating FSGS and COLL from Normal and MCD. Class comparison analysis of FSGS + COLL combined versus Normal + MCD revealed 316 significantly differentially regulated genes (134 up-regulated, 182 down-regulated). Among the differentially regulated genes were those known to be part of the slit diaphragm junctional complex and those previously described in the dysregulated podocyte phenotype. Analysis based on Gene Ontology categories revealed overrepresented biological processes of development, differentiation and morphogenesis, cell motility and migration, cytoskeleton organization, and signal transduction. Transcription factors associated with developmental processes were heavily overrepresented, indicating the importance of reactivation of developmental programs in the pathogenesis of FSGS. Our findings reveal novel insights into the molecular pathogenesis of glomerular injury and structural degeneration in FSGS.

Glomerular structure and function require paracrine, not autocrine, VEGF-VEGFR-2 signaling

VEGF is a potent vascular growth factor produced by podocytes in the developing and mature glomerulus. Specific deletion of VEGF from podocytes causes glomerular abnormalities including profound endothelial cell injury, suggesting that paracrine signaling is critical for maintaining the glomerular filtration barrier (GFB). However, it is not clear whether normal GFB function also requires autocrine VEGF signaling in podocytes. In this study, we sought to determine whether an autocrine VEGF-VEGFR-2 loop in podocytes contributes to the maintenance of the GFB in vivo. We found that induced, whole-body deletion of VEGFR-2 caused marked abnormalities in the kidney and also other tissues, including the heart and liver. By contrast, podocyte-specific deletion of the VEGFR-2 receptor had no effect on glomerular development or function even up to 6 months old. Unlike cell culture models, enhanced expression of VEGF by podocytes in vivo caused foot process fusion and alterations in slit diaphragm-associated proteins; however, inhibition of VEGFR-2 could not rescue this defect. Although VEGFR-2 was dispensable in the podocyte, glomerular endothelial cells depended on VEGFR-2 expression: postnatal deletion of the receptor resulted in global defects in the glomerular microvasculature. Taken together, our results provide strong evidence for dominant actions of a paracrine VEGF-VEGFR-2 signaling loop both in the developing and in the filtering glomerulus. VEGF produced by the podocyte regulates the structure and function of the adjacent endothelial cell.

Molecular anatomy of the kidney: what have we learned from gene expression and functional genomics?

The discipline of paediatric nephrology encompasses the congenital nephritic syndromes, renal dysplasias, neonatal renal tumours, early onset cystic disease, tubulopathies and vesicoureteric reflux, all of which arise due to defects in normal kidney development. Indeed, congenital anomalies of the kidney and urinary tract (CAKUT) represent 20-30% of prenatal anomalies, occurring in 1 in 500 births. Developmental biologists have studied the anatomical and morphogenetic processes involved in kidney development for the last five decades. However, with the advent of transgenic mice, the sequencing of the genome, improvements in mutation detection and the advent of functional genomics, our understanding of the molecular basis of kidney development has grown significantly. Here we discuss how the advent of new genetic and genomics approaches has added to our understanding of kidney development and paediatric renal disease, as well as identifying areas in which we are still lacking knowledge.

Uncovering multiple molecular targets for caffeine using a drug target validation strategy combining A 2A receptor knockout mice with microarray profiling

Caffeine is the most widely consumed psychoactive substance and has complex pharmacological actions in brain. In this study, we employed a novel drug target validation strategy to uncover the multiple molecular targets of caffeine using combined A(2A) receptor (A(2A)R) knockouts (KO) and microarray profiling. Caffeine (10 mg/kg) elicited a distinct profile of striatal gene expression in WT mice compared with that by A(2A)R gene deletion or by administering caffeine into A(2A)R KO mice. Thus, A(2A)Rs are required but not sufficient to elicit the striatal gene expression by caffeine (10 mg/kg). Caffeine (50 mg/kg) induced complex expression patterns with three distinct sets of striatal genes: 1) one subset overlapped with those elicited by genetic deletion of A(2A)Rs; 2) the second subset elicited by caffeine in WT as well as A(2A)R KO mice; and 3) the third subset elicited by caffeine only in A(2A)R KO mice. Furthermore, striatal gene sets elicited by the phosphodiesterase (PDE) inhibitor rolipram and the GABA(A) receptor antagonist bicucullin, overlapped with the distinct subsets of striatal genes elicited by caffeine (50 mg/kg) administered to A(2A)R KO mice. Finally, Gene Set Enrichment Analysis reveals that adipocyte differentiation/insulin signaling is highly enriched in the striatal gene sets elicited by both low and high doses of caffeine. The identification of these distinct striatal gene populations and their corresponding multiple molecular targets, including A(2A)R, non-A(2A)R (possibly A(1)Rs and pathways associated with PDE and GABA(A)R) and their interactions, and the cellular pathways affected by low and high doses of caffeine, provides molecular insights into the acute pharmacological effects of caffeine in the brain.

Glomerular type 1 angiotensin receptors augment kidney injury and inflammation in murine autoimmune nephritis

Studies in humans and animal models indicate a key contribution of angiotensin II to the pathogenesis of glomerular diseases. To examine the role of type 1 angiotensin (AT1) receptors in glomerular inflammation associated with autoimmune disease, we generated MRL-Faslpr/lpr (lpr) mice lacking the major murine type 1 angiotensin receptor (AT1A); lpr mice develop a generalized autoimmune disease with glomerulonephritis that resembles SLE. Surprisingly, AT1A deficiency was not protective against disease but instead substantially accelerated mortality, proteinuria, and kidney pathology. Increased disease severity was not a direct effect of immune cells, since transplantation of AT1A-deficient bone marrow did not affect survival. Moreover, autoimmune injury in extrarenal tissues, including skin, heart, and joints, was unaffected by AT1A deficiency. In murine systems, there is a second type 1 angiotensin receptor isoform, AT1B, and its expression is especially prominent in the renal glomerulus within podocytes. Further, expression of renin was enhanced in kidneys of AT1A-deficient lpr mice, and they showed evidence of exaggerated AT1B receptor activation, including substantially increased podocyte injury and expression of inflammatory mediators. Administration of losartan, which blocks all type 1 angiotensin receptors, reduced markers of kidney disease, including proteinuria, glomerular pathology, and cytokine mRNA expression. Since AT1A-deficient lpr mice had low blood pressure, these findings suggest that activation of type 1 angiotensin receptors in the glomerulus is sufficient to accelerate renal injury and inflammation in the absence of hypertension.

Contribution of guanine nucleotide exchange factor Vav2 to hyperhomocysteinemic glomerulosclerosis in rats

We currently reported that Vav2, a member of the guanine nucleotide exchange factor-Vav subfamily, participates in homocysteine-induced increases in Rac1 activity and consequent activation of NADPH oxidase in rat mesangial cells. However, the physiological relevance of this cellular action of Vav2 remains unknown. The present study tested a hypothesis that Vav2 importantly mediates the injurious action of homocysteine on glomeruli and thereby contributes to the development of glomerulosclerosis during hyperhomocysteinemia. We found that, among Vav members, Vav2 was abundantly expressed in glomeruli. When Vav2 short hairpin RNA was transfected into the kidneys of Sprague-Dawley rats, hyperhomocysteinemia induced by folate-free diet failed to significantly enhance Rac1 activity and increase NADPH-dependent superoxide production. In these rats with silenced renal Vav2 gene, glomerular injury during hyperhomocysteinemia was markedly attenuated compared with those rats only receiving mock vector transfection, as shown by ameliorated albuminuria and extracellular matrix metabolism. In the rat kidneys with transfection of a dominant-active Vav2 variant (onco-Vav2), we found that overexpression of Vav2 led to significant increases in Rac1 activity, superoxide production, and glomerular injury, which was similar to that induced by hyperhomocysteinemia. However, this Vav2 overexpression was unable to further enhance homocysteine-induced glomerular injury. We concluded that Vav2-mediated activation of NADPH oxidase is an important initiating mechanism resulting in hyperhomocysteinemic glomerular injury through enhanced local oxidative stress.

The lmx1b gene is pivotal in glomus development in Xenopus laevis

We have previously shown that lmx1b, a LIM homeodomain protein, is expressed in the pronephric glomus. We now show temporal and spatial expression patterns of lmx1b and its potential binding partners in both dissected pronephric anlagen and in individual dissected components of stage 42 pronephroi. Morpholino oligonucleotide knock-down of lmx1b establishes a role for lmx1b in the development of the pronephric components. Depletion of lmx1b results in the formation of a glomus with reduced size. Pronephric tubules were also shown to be reduced in structure and/or coiling whereas more distal tubule structure was unaffected. Over-expression of lmx1b mRNA resulted in no significant phenotype. Given that lmx1b protein is known to function as a heterodimer, we have over-expressed lmx1b mRNA alone or in combination with potential interacting molecules and analysed the effects on kidney structures. Phenotypes observed by over-expression of lim1 and ldb1 are partially rescued by co-injection with lmx1b mRNA. Animal cap experiments confirm that co-injection of lmx1b with potential binding partners can up-regulate pronephric molecular markers suggesting that lmx1b lies upstream of wt1 in the gene network controlling glomus differentiation. This places lmx1b in a genetic hierarchy involved in pronephros development and suggests that it is the balance in levels of binding partners together with restricted expression domains of lmx1b and lim1 which influences differentiation into glomus or tubule derivatives in vivo.

Ectopic notch activation in developing podocytes causes glomerulosclerosis

Genetic evidence supports an early role for Notch signaling in the fate of podocytes during glomerular development. Decreased expression of Notch transcriptional targets in developing podocytes after the determination of cell fate suggests that constitutive Notch signaling may oppose podocyte differentiation. This study determined the effects of constitutive Notch signaling on podocyte differentiation by ectopically expressing Notch's intracellular domain (NOTCH-IC), the biologically active, intracellular product of proteolytic cleavage of the Notch receptor, in developing podocytes of transgenic mice. Histologic and molecular analyses revealed normal glomerular morphology and expression of podocyte markers in newborn NOTCH-IC-expressing mice; however, mice developed severe proteinuria and showed evidence of progressive glomerulosclerosis at 2 wk after birth. Features of mature podocytes were lost: Foot processes were effaced; expression of Wt1, Nphs1, and Nphs2 was downregulated; cell-cycle re-entry was induced; and the expression of Pax2 was increased. In contrast, mice with podocyte-specific inactivation of Rbpsuh, which encodes a protein essential for canonical Notch signaling, seemed normal. In addition, the damaging effects of NOTCH-IC expression were prevented in transgenic mice after simultaneous conditional inactivation of Rbpsuh in murine podocytes. These results suggest that Notch signaling is dispensable during terminal differentiation of podocytes but that constitutive (or inappropriate) Notch signaling is deleterious, leading to glomerulosclerosis.

How do mesangial and endothelial cells form the glomerular tuft?

The glomerular capillary tuft is a highly intricate and specialized microvascular bed that filters plasma water and solute to form urine. The mature glomerulus contains four cell types: Parietal epithelial cells that form Bowman's capsule, podocytes that cover the outermost layer of the glomerular filtration barrier, glycocalyx-coated fenestrated endothelial cells that are in direct contact with blood, and mesangial cells that sit between the capillary loops. Filtration begins only after the influx and organization of endothelial and mesangial cells in the developing glomerulus. Tightly coordinated movement and cross-talk between these cell types is required for the formation of a functional glomerular filtration barrier, and disruption of these processes has devastating consequences for early life. Current concepts of the role of mesangial and endothelial cells in formation of the capillary tuft are reviewed here.

Maternal diabetes modulates renal morphogenesis in offspring

Maternal diabetes leads to an adverse in utero environment, but whether maternal diabetes impairs nephrogenesis is unknown. Diabetes was induced with streptozotocin in pregnant Hoxb7-green fluorescence protein mice at embryonic day 13, and the offspring were examined at several time points after birth. Compared with offspring of nondiabetic controls, offspring of diabetic mice had lower body weight, body size, kidney weight, and nephron number. The observed renal dysmorphogenesis may be the result of increased apoptosis, because immunohistochemical analysis revealed significantly more apoptotic podocytes as well as increased active caspase-3 immunostaining in the renal tubules compared with control mice. Regarding potential mediators of these differences, offspring of diabetic mice had increased expression of intrarenal angiotensinogen and renin mRNA, upregulation of NF-kappaB isoforms p50 and p65, and activation of the NF-kappaB pathway. In conclusion, maternal diabetes impairs nephrogenesis, possibly via enhanced intrarenal activation of the renin-angiotensin system and NF-kappaB signaling.

Pod1 induces myofibroblast differentiation in mesenchymal progenitor cells from mouse kidney

The class II basic helix-loop-helix (bHLH) transcription factor Pod1 is expressed in mesenchymal cells including smooth muscle progenitors during development and in interstitial cells in adult organs. To determine the role of Pod1 in mesenchymal cell smooth muscle and myofibroblast differentiation, we examined a kidney progenitor cell line (4E) that endogenously expresses Pod1 and its class I bHLH partner E2A. In vitro-translated Pod1 co-immunoprecipitated E2A and increased E2A binding to a calponin promoter E-box sequence as determined by an electrophoresis mobility shift assay (EMSA). Overexpression of Pod1 and E2A resulted in increased smooth muscle and myofibroblast gene expression including calponin, SM22alpha, alphaSMA, fibronectin, and connective tissue growth factor (CTGF) compared with overexpression of E2A alone. Suppression of Pod1 by siRNA resulted in increased cell proliferation and reduced expression of alphaSMA, fibronectin, and CTGF, and myofibroblast secreted proteins including pro-fibrotic cytokines and inhibitors of matrix metalloproteinases. Examination of the signaling pathways for myofibroblast differentiation including Rho/Rho kinase and p38 MAPK showed that inhibition of actin polymerization by Rho kinase inhibitors decreased nuclear Pod1 levels while inhibition of p38 MAPK decreased Pod1 expression. These results indicate that Pod1 increases myofibroblast differentiation in combination with E2A and promotes a myofibroblast phenotype in mesenchymal progenitor cells.

Role of transcription factors in podocytes

Despite a wealth of information on structural proteins, comparatively little is known on the transcriptional regulation of podocyte structure and function. In this review we will highlight those transcription factors which, by gene inactivation or classical transgenic experiments, have been shown to be essential for podocytes or probably will turn out to be so. The tumor suppressor protein WT1 is not only indispensable for the initial stages of kidney development, but also very likely maintains the integrity of the fully differentiated podocyte. In the kidney, the LIM homeodomain transcription factor LMX1B is specifically synthesized in podocytes, and mutations in LMX1B lead to nail-patella syndrome and the associated nephropathy. Other transcription factors such as hypoxia-inducible factors and PAX2 are likely to play a role in podocytes, whereas the significance of others, e.g. of POD1 and CITED2, is more speculative at this point.

Transcriptional regulation of podocyte disease

The podocyte is a highly specialized visceral epithelial cell that forms the outermost layer of the glomerular capillary loop and plays a critical role in the maintenance of the glomerular filtration barrier. Several transcriptional factors regulate the podocyte function under normal and disease conditions. In this review, the role of Wilms tumor 1 (WT1), LIM homeobox transcription factor 1, beta (Lmx1b), pod1, pax-2, kreisler, nuclear factor-kappa B (NF-kappaB), smad7, and zinc fingers and homeoboxes (ZHX) proteins in the development of podocyte disease is outlined. The regulation of several important podocyte genes, including transcriptional factors, by ZHX proteins, their predominant non-nuclear localization in the normal in vivo podocyte, and changes in ZHX expression related to the development of minimal change disease and focal and segmental glomerulosclerosis are discussed. Finally, some future therapeutic strategies for glomerular disease are proposed.

Loss of the tumor suppressor Vhlh leads to upregulation of Cxcr4 and rapidly progressive glomerulonephritis in mice

Rapidly progressive glomerulonephritis (RPGN) is a clinical syndrome characterized by loss of renal function within days to weeks and by glomerular crescents on biopsy. The pathogenesis of this disease is unclear, but circulating factors are believed to have a major role. Here, we show that deletion of the Von Hippel-Lindau gene (Vhlh) from intrinsic glomerular cells of mice is sufficient to initiate a necrotizing crescentic glomerulonephritis and the clinical features that accompany RPGN. Loss of Vhlh leads to stabilization of hypoxia-inducible factor alpha subunits (HIFs). Using gene expression profiling, we identified de novo expression of the HIF target gene Cxcr4 (ref. 3) in glomeruli from both mice and humans with RPGN. The course of RPGN is markedly improved in mice treated with a blocking antibody to Cxcr4, whereas overexpression of Cxcr4 alone in podocytes of transgenic mice is sufficient to cause glomerular disease. Collectively, these results indicate an alternative mechanism for the pathogenesis of RPGN and glomerular disease in an animal model and suggest novel molecular pathways for intervention in this disease.

Large-scale identification of genes implicated in kidney glomerulus development and function

To advance our understanding of development, function and diseases in the kidney glomerulus, we have established and large-scale sequenced cDNA libraries from mouse glomeruli at different stages of development, resulting in a catalogue of 6053 different genes. The glomerular cDNA clones were arrayed and hybridized against a series of labeled targets from isolated glomeruli, non-glomerular kidney tissue, FACS-sorted podocytes and brain capillaries, which identified over 300 glomerular cell-enriched transcripts, some of which were further sublocalized to podocytes, mesangial cells and juxtaglomerular cells by in situ hybridization. For the earliest podocyte marker identified, Foxc2, knockout mice were used to analyze the role of this protein during glomerular development. We show that Foxc2 controls the expression of a distinct set of podocyte genes involved in podocyte differentiation and glomerular basement membrane maturation. The primary podocyte defects also cause abnormal differentiation and organization of the glomerular vascular cells. We surmise that studies on the other novel glomerulus-enriched transcripts identified in this study will provide new insight into glomerular development and pathomechanisms of disease.